AN APPROXIMATION TO HYDROPHOBIC ATTRACTION FOR MOLECULAR-DYNAMICS OF SELF-ASSEMBLED SURFACTANT AGGREGATES

The measured long-range force between hydrophobic surfaces coated with surfactants is several orders of magnitude larger than the expected v an der Waals attraction. Hydrophobic attraction of a magnitude similar to that found by experiment was applied to molecular dynamics simulat ions of surfactant micelles and bilayers. The force was approximated b y multiplying normally accepted van der Waals attraction between hydro carbon chains of surfactants by scaling factors within a commercial mo lecular dynamics software package. Micelles of sodium octanoate and N- octylbetaine and a bilayer of didodecyldimethylammonium bromide were s imulated with all-atom and united-atom hydrocarbon chains, with and wi thout water. Results were compared to simulations without the hydropho bic attraction. Inclusion of the approximate hydrophobic force provide d dynamic aggregate structures for all simulations which more closely resembled models supported by experimental data, whether water was pre sent or absent. Scaling of the hydrophobic attraction was used to prov ide simulations of gel and liquid crystal phases of the bilayer.